There is heretofore known a gas sensor having a sensor element for detecting a specific gas component in exhaust gas of a car or the like. The sensor element of such a gas sensor is formed as a plate-like element having at least one layer of solid electrolyte clamped between a pair of electrodes and detects the concentration of a specific gas (e.g. oxygen) in exhaust gas. Because the solid electrolyte is not activated when the temperature is low, a heater for heating the sensor element to activate it is generally provided near the sensor element. For example, a product having a laminate structure in which a plate-like heater and a sensor element are baked so as to be integrated with each other is known as a heater integral type senor element.
In the condition that such a sensor element is inserted into an axial hole of a ceramic sleeve (element side electrical porcelain), the sensor element is glass-sealed to thereby be held in the sleeve. The sleeve is held in a metal shell so that the sensor element can be finally incorporated in the metal shell. To take an output from the sensor element, an electrode holder (atmospheric air side electrical porcelain) is put so that electrode terminal portions provided on upper and lower surfaces respectively on the rear end side of the sensor element are covered with the electrode holder. Connection terminals are provided in the electrode holder so that the connection terminals abut on the electrode terminal portions of the sensor element. When the sensor element and electrode springs are clamped from opposite surfaces of the sensor element, electrical connection between the electrode terminal portions and the connection terminals can be ensured.
If the electrode holder and the sleeve are fitted to each other on this occasion, the two are aligned with each other so that the electrode holder is prevented from being disposed so as to be inclined with respect to the sleeve. For this reason, the rear end portion of the sensor element inserted in the electrode holder is prevented from being broken by collision with the inner surface of the electrode holder (e.g. see Patent Document 1).
Patent Document 1: Japanese Patent Laid-Open No. 2003-43004